A large number of computers have been and are being connected to a communication network to form a system such that each of the computers can be connected to many and unspecified persons over a communication path. Therefore, there is the possibility that also electronic information stored in an external storage apparatus of a computer such as a hard disk apparatus may be accessed by a third party having no authority over a communication path and stolen or altered.
Also transmission of electronic information over a communication path such as exchange of personal information by an electronic mail and so forth, distribution of an application program such as a game program or a business program or distribution of data extracted from a database and edited has been and is increasing. Where communication environments open to the outside are used for such electronic information exchange, there is the possibility that a third party who is not a receiving party may acquire electronic information being communicated through an intercepting or stealing action and utilize the electronic information. Particularly where information is distributed for pay or information relating to privacy is transmitted, it is necessary to take a countermeasure so that electronic information being communicated may not be stolen readily.
In order to disable utilization of electronic information by a third party having no relation even if the third party acquires the electronic information, a method is used to assure the secrecy of electronic information through encipherment of the electronic information. Encipherment techniques developed for the object just described include various systems such as encipherment systems which use a symmetrical key and another encipherment systems which use an asymmetrical key.
However, even if such encipherment techniques are used, since stored electronic information or electronic information being transmitted includes all information, if someone acquires a decipherment method through some means such as deciphering of the cipher, then the person can decipher the cipher readily to acquire the useful information. Also alteration or counterfeiting is possible, and attention must always be paid to whether or not information extracted or received keeps true and correct information. Particularly where electronic information for which high security is required such as authentication information of the person itself is stored or transmitted, the conventional methods are not free from anxiety.
If information stored or being communicated is subject to alteration or missing, then most of the information extracted or received cannot be utilized correctly, and use of the incorrect information as it is may give rise to some trouble. Also the fact itself that information is known to a third party sometimes matters. Accordingly, a convenient technique for confirming that received electronic information has the identity with that which has been forwarded and for confirming that electronic information is used legally is demanded.
Therefore, it is an object of the present invention to provide a technique of assuring the security of electronic information by working electronic information to be stored or transmitted so that, even if the electronic information stored or being transmitted is stolen, it cannot be utilized thereby to decrease the value of the information and to provide a method of assuring the genuineness of information which a user has extracted or received to restore.